The present invention relates to methods for assessing navigational capacity and to their use in diagnosing spatial disorientation in neurodegenerative diseases.
It is known that Alzheimer's disease (AD) is characterized by memory loss in the setting of other progressive behavioral and cognitive impairments. It is also known that spatial disorientation affects more than one-third of AD patients early in the illness {Henderson}. Spatial disorientation is disabling because it impairs independent navigation and interferes with the capacity to drive safely and maintain a separate household.
Spatial orientation relies on the integration of perceptual cues about location and self-movement. Location cues orient the observer by relating recognized landmarks to remembered positions in a spatial framework that defines their proximity to other landmarks. Self-movement cues orient the observer relative to a starting position by tracking successive movements through path integration. Orientation by landmarks relies on access to a long-term cognitive map of the environment, whereas orientation by self-movement is independent of the observer's familiarity with a site.
In mammals, cognitive mapping is attributed to the hippocampus where individual neurons represent particular locations in the environment. As the hippocampus is involved early in the course of AD, it is likely that orientation by landmarks might suffer early impairment and leave patients relying on path integration. As path integration might fail, these patients are left suffering spatial disorientation.
The present inventors have shown previously that spatial disorientation in AD is related to impaired ability to see the patterned visual motion of optic flow that supports self-movement perception and orientation by path integration.
To help characterize navigational capacity, methods are needed that test the relationship between remembered locations and spatial orientation in human subjects, especially those suffering from neurodegenerative diseases such as AD.